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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .con{
            width: 400px;
            height: 400px;
            border: 1px dashed black;
            position: relative;
        }
        .item{
            position: absolute;
            /* top: 100px; */
            /* margin: 20px; */
            background-color: aquamarine;
            /* z-index: -1; */
        }
        .item2{
            /* z-index: -10; */
            background-color: blueviolet;
        }
    </style>
</head>
<body>
    <div class="con">
        <div class="item">
            绝对定位
        </div>
        <div class="item2">
            佬，菜，带
        </div>
    </div>
</body>
</html>